Using SISO decoder feedback to produce symbol probabilities for use in wireless communications that utilize single encoder turbo coding and transmit diversity

ABSTRACT

An apparatus and method for transmitting and receiving a bit stream. On the transmission side, coded bits (Y.sub.t) and an interleaved version of the coded bits (X.sub.t) are separately modulated and transmitted. On the reception side, a priori output probabilities produced by a probability generator ( 34 ) are combined ( 112 ) and then input to a SISO decoder ( 111 ). Combined a posteriori output probabilities ( 115 ) produced by the SISO decoder are split ( 113 ) and then fed back to the probability generator.

This application is a Divisional of application Ser. No. 10/037,179,filed Oct. 23, 2001, now U.S. Pat. No. 7,120,213 which claims priorityunder 35 USC 119(e)(1) of copending U.S. provisional application No.60/244,043 filed on Oct. 27, 2000. This application contains subjectmatter related to subject matter disclosed in U.S. Ser. No. 09/925,077filed on Aug. 8, 2001, which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates generally to wireless communications and, moreparticularly, to wireless communications that utilize turbo coding andtransmit diversity.

BACKGROUND OF THE INVENTION

Each of the documents listed below is referred to herein by thecorresponding number enclosed in square brackets to the left of thedocument. Each of these documents is also incorporated herein byreference.

-   [1] Y. Liu, M. P. Fitz, and O. Y. Takeshita, “Qpsk space-time turbo    codes,” in IEEE ICC, June 2000.-   [2] X. Li and J. A. Ritcey, “Bit-interleaved coded modulation with    iterative decoding,” using soft feedback, “Electronic Letters, vol.    34, pp. 942-943, 4 Mar. 1998.-   [3] X. Li and J. A. Ritcey, “Bit-interleaved coded modulation with    iterative decoding,” in IEEE ICC, vol. 2, pp. 858-863, June 1999.-   [4] X. Li and J. A. Ritcey, “Trellis-coded modulation with bit    interleaving and iterative decoding,” IEEE Journal on Selected Areas    in Communications, vol. 17, pp. 715-724, April 1999.-   [5] X. Li and J. A. Ritcey, “Bit-interleaved coded modulation with    iterative decoding,” IEEE Communications Letters, vol. 1, pp.    169-171, November 1997.-   [6] V. Tarokh, N. Seshadri, and A. R. Calderbank, “Space-Time Codes    for High Data Rate Wireless Communication: Performance Criterion and    Code Construction,” in IEEE Transactions on information theory, vol.    44, No. 2, pp. 744-765, March 1998.-   [7] A. R. Hammons and H. E. Gamal, “On the Theory of Space-Time    Codes for PSK Modulation,” in IEEE Transactions on information    theory, vol. 2, No. 2, pp. 524-542, March 2000.

Coding and interleaving techniques are often used in wirelesscommunication systems to improve the communication performance. FIG. 1illustrates an example of a conventional wireless communication systemdescribed in [1]. This example implements turbo coding by using twoconvolutional coders (CC). One of the convolutional coders receives atits input the data stream that is to be transmitted, and the otherconvolutional coder receives at its input an interleaved (see 10)version of the data stream. The outputs of the convolutional coders arethen modulated using QPSK (Quadrature Phase Shift Keying) andtransmitted by respective transmit antennas. At the receiver, the signalfrom the antenna is input to a probability generator which generatessymbol (or bit) probabilities. These symbol probabilities are fed tosoft-input, soft-output (SISO) decoders that iterate to get estimates ofthe transmitted symbols (or bits). The SISO decoders use knowledge ofthe trellis of the convolutional coders to produce the estimates.

FIG. 2 illustrates an example of a conventional wireless communicationsystem described in [2] and [3]. The system of FIG. 2 uses a singleconvolutional coder and an interleaver 21 before modulation andtransmission by a single antenna. At the receiver, the signal from theantenna is demodulated and de-interleaved (see 22), and is then input toa SISO decoder. The a posteriori symbol probabilities output from theSISO decoder are interleaved (see 23) and fed back into the demodulatorto get a better estimate of the symbol probabilities. This loop isiterated over. Systems similar to the one illustrated in FIG. 2 havealso been suggested in [4] and [5], but those systems implement harddecoding decisions instead of soft decisions.

FIG. 8 illustrates an example of a conventional wireless communicationsystem described in [6]. In this example, bits are encoded with a singleencoder, and separate sets of the encoded bits are applied to respectivemodulators in separate branches. The modulators perform constellationmapping, and the separate branches permit transmit diversity. Specialcare is exercised in order to provide a full diversity stream. At thereceiving end, conventional Viterbi decoding is performed. The work in[6] was followed by the work in [7], wherein it is demonstrated that,for all BPSK constellations, it is very easy to achieve diversity, andthat coding advantage should be a primary optimization goal.

It is desirable in view of the foregoing to provide for improvedperformance in wireless communication systems that utilize turbo codingand transmit diversity.

According to the invention, coded bits and an interleaved version of thecoded bits are separately modulated and transmitted. On the receiverside, a priori output probabilities produced by the probabilitygenerator are combined and then input to a SISO decoder, and combined aposteriori output probabilities produced by the SISO decoder are splitand then fed back to the probability generator. This advantageouslypermits the probability generator to produce an improved estimate of thereceived symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional wireless communication system whichutilizes interleaving, turbo coding and transmit diversity.

FIG. 2 illustrates a conventional wireless communication system thatutilizes turbo coding, interleaving and feedback of a posterioriprobabilities from a SISO decoder.

FIG. 3 diagrammatically illustrates exemplary embodiments of wirelesscommunication systems which utilize turbo coding, interleaving, transmitdiversity and a posteriori probability feedback according to theinvention.

FIG. 4 diagrammatically illustrates exemplary embodiments of theprobability generator of FIG. 3.

FIG. 5 illustrates exemplary operations which can be performed by thereceiver of FIG. 3.

FIG. 6 diagrammatically illustrates further exemplary embodiments ofwireless communication systems which utilize interleaving, turbo coding,transmit diversity and a posteriori probability feedback according tothe invention.

FIG. 7 illustrates exemplary simulation results for the systems of FIGS.1, 3 and 6.

FIG. 8 illustrates a conventional wireless communication system whichutilizes a single encoder and transmit diversity.

FIG. 9 diagrammatically illustrates exemplary embodiments of a wirelesscommunication transmission apparatus which utilizes a single encoderaccording to the invention.

FIG. 10 diagrammatically illustrates exemplary embodiments of a wirelesscommunication receiving apparatus that is cooperable with the wirelesscommunication transmission apparatus of FIG. 9.

FIG. 11 illustrates exemplary operations which can be performed by thewireless communication receiving apparatus of FIG. 10.

FIG. 12 illustrates exemplary simulation results which compare theperformance of the system of FIGS. 9 and 10 to the performance of theconventional system of FIG. 8.

DETAILED DESCRIPTION

Referring again to FIG. 1, the symbol Z_(t) received by the antenna ofthe receiver 12 at time t can be expressed as a function of thecorresponding symbols or bits X_(t) and Y_(t) produced by the respectiveconvolutional coders of the transmitter 11, and the fadingcharacteristics of the respective wireless communication channelsthrough which X_(t) and Y_(t) are transmitted to the receiver 12. Thefading characteristics (or coefficients) are illustrated by fadingparameters α and β in FIG. 1. Accordingly, the symbol value received bythe antenna of the receiver 12 can be expressed as followsZ _(t) =αX _(t) +βY _(t) +n _(t),  (1)where n_(t) represents noise in the wireless communication channels. At13, the probability generator 15 produces, for all possible values C_(X)that X_(t) can assume at time t, the following probabilityP(X _(t) =C _(X) |Z _(t) =C _(Z))  (2)Expression (2) above represents the probability that X_(t)=C_(X) giventhat the received symbol or bit value Z_(t)=C_(Z). At 14, theprobability generator 15 produces similar probabilities for all possiblevalues C_(y) of Y_(t), namelyP(Y _(t) =C _(Y) |Z _(t) =C _(Z))  (3)

Taking the probability defined in Expression (2) above as an example,and applying Bayes' Rule, Expression (2) can be written as followsP(Z _(t) =C _(Z) |X _(t) =C _(X))P(X _(t) =C _(X))/P(Z _(t) =C_(Z))  (4)

In practice, for an iterative loop, the probability given by Expression(2) is generated under the assumption that nothing is known in advanceabout the statistics of X_(t). This is called the extrinsic probabilityand ensures that only “new” information is used to generate data thatwill be fed back. Therefore, P(X_(t)=C_(x)) can be eliminated fromExpression (4). The denominator of Expression (4) can also be eliminatedbecause it merely represents the probability that Z_(t)=C_(Z) at time t,which is merely a constant value that operates only as a scaling factor.Thus, eliminating the aforementioned extrinsic factor and theaforementioned scaling factor from Expression (4) leavesP(Z _(t) =C _(Z) |X _(t) =C _(X))  (5)

Using known probability theory, Expression (5) can be rewritten asfollows

$\begin{matrix}{\sum\limits_{C_{Y}}{{P( {Z_{t} = {{C_{Z}❘X_{t}} = {{C_{X}\mspace{14mu}{and}\mspace{14mu} Y_{t}} = C_{Y}}}} )}{P( {Y_{t} = {{C_{Y}❘X_{t}} = C_{X}}} )}}} & (6)\end{matrix}$

Referring again to Equation (1) above, the leftmost probability ofExpression (6) can be rewritten as followsP(n _(t) =C _(Z) −αC _(X) −βC _(Y))  (7)

Substituting Expression (7) into Expression (6) gives

$\begin{matrix}{\sum\limits_{C_{Y}}{{P( {n_{t} = {C_{Z} - {\alpha\; C_{X}} - {\beta\; C_{Y}}}} )}{P( {Y_{t} = {{C_{Y}❘X_{t}} = C_{X}}} )}}} & (8)\end{matrix}$

Thus, Expression (2) above can be rewritten as Expression (8) above.

The noise n_(t) in Expression 8 can be modeled as a Gaussian randomvariable, and the fading parameters α and β can be readily estimated.Thus, given that the received symbol Z_(t)=C_(Z) is known, values of theleftmost probability in Expression 8 can be easily calculated for allpossible values of C_(X) and C_(Y). The values of the rightmostprobability of Expression (8) are provided according to the invention asthe a posteriori output probabilities from a SISO decoder, as describedin more detail below.

Using reasoning analogous to that given above for rewriting Expression(2) as Expression (8), Expression (3) above can be rewritten as follows

$\begin{matrix}{\sum\limits_{C_{X}}{{P( {n_{t} = {C_{Z} - {\alpha\; C_{X}} - {\beta\; C_{Y}}}} )}{P( {X_{t} = {{C_{X}❘Y_{t}} = C_{Y}}} )}}} & (9)\end{matrix}$

As mentioned above with respect to Expression (8), the leftmostprobability of Expression (9) can be easily calculated for a known valueof C_(Z) and all possible values of C_(X) and C_(Y). Also analogous tothe discussion of Expression (8) above, the values of the rightmostprobability of Expression (9) are provided according to the invention asa posteriori output probabilities of a SISO decoder.

Referring now to FIG. 3, in exemplary wireless communication systemembodiments according to the invention, a receiver 31 includes aprobability generator 34 coupled to an antenna which receives symbolZ_(t) from a transmitter that employs transmit diversity, for examplethe transmitter 11 of FIG. 1. The probability generator 34 calculatesthe values of the leftmost probability in Expressions (8) and (9). Atits input 47, the probability generator receives (as feedback) from SISOdecoder 35 the values of the rightmost probability of Expression (9). Atits input 48, the probability generator 34 receives (as feedback) fromthe SISO decoder 36 the values of the rightmost probability ofExpression (8). Having calculated the values of the leftmost probabilityof Expressions (8) and (9), and having received the values of therightmost probabilities of Expressions (8) and (9) from the SISOdecoders 36 and 35, respectively, the probability generator 34 performsthe summation of Expression (8) to produce at its output 45 the valuesof the probability of Expression (2), and also performs the summation ofExpression (9) to produce at its output 46 the values of the probabilityof Expression (3).

The outputs 45 and 46 provide a priori output probabilities to the SISOdecoders 35 and 36. The decoder 35 operates with respect to X_(t) andthe decoder 36 operates with respect to Y_(t). The SISO decoders 35 and36 use their respective a priori output probabilities to producerespective a posteriori input probabilities. The a posteriori inputprobabilities produced by SISO decoder 35 are interleaved at 38(corresponding to the interleaver in the transmitter 11) and the resultsare provided as a priori input probabilities to the SISO decoder 36.Similarly, the a posteriori input probabilities produced by the SISOdecoder 36 are de-interleaved at 37 (again corresponding to theinterleaver of the transmitter 11) and the results are provided as apriori input probabilities to the SISO decoder 35. The a posterioriinput probabilities produced by the SISO decoder 35 are also provided toa decision maker which can use conventional techniques to decide theinput symbol (as seen by the corresponding coder 16) based on the aposteriori input probabilities.

The output probabilities provided to (a priori) and produced by (aposteriori) the SISO decoder 35 represent respective probabilities thatthe symbol X_(t) as output from the convolutional coder 16 hasrespective ones of a plurality of possible values. Similarly, the inputprobabilities provided to (a priori) and produced by (a posteriori) SISOdecoder 35 represent respective probabilities that the symbol that wasinput to the convolutional coder 16 to produce X_(t) has respective onesof a plurality of possible values. The SISO decoder 36 functionsanalogously with respect to the symbol Y_(t) and the convolutional coder17. Each SISO decoder uses the a priori probabilities (input and output)provided thereto together with knowledge of the trellis used by thecorresponding convolutional coder to produce corresponding a posterioriprobabilities (output and input). In some embodiments, each coder 16 and17 uses the same trellis.

FIG. 4 diagrammatically illustrates exemplary embodiments of theprobability generator 34 of FIG. 3. A fading parameter estimator 42provides estimates α′ and β′ of the fading parameters α and β of FIG. 3using, for example, any desired conventional technique. A calculationapparatus 41 receives these estimated fading parameters, and also hasaccess (e.g. from look-up table values) to the probability of the noiseparameter n_(t), which can be modeled, for example, as a Gaussian randomvariable. The calculation apparatus 41 knows the value of C_(Z) (simplythe received value) in Expressions (8) and (9), and thus can calculatethe values of the leftmost probability in Expressions (8) and (9) usingthe estimated fading parameters α′ and β′. Thus, the calculationapparatus 41 produces at 49 the values of the leftmost probability ofExpressions (8) and (9). These values are input to combiners 43 and 44.

The combiner 43 receives at 47 the a posteriori output probabilitiesproduced by SISO decoder 35, and the combiner 44 receives at 48 the aposteriori output probabilities produced by SISO decoder 36. The valuesreceived at 47 represent the values of the rightmost probability inExpression (9) and the values received at 48 represent the values of therightmost probability in Expression (8). The combiner 43 operates tocombine the values that it receives at 49 and 47 in the manner shown inExpression (8), namely multiplying the values together and summing theresulting products over all possible values of C_(Y). Similarly, thecombiner 44 combines the values that it receives at 49 and 48 as shownby Expression (9) above, namely multiplying the values together andsumming the resulting products over all possible values of C_(X). Thecombiner 43 produces at 46 the values of the probability shown inExpression (3), and the combiner 44 produces at 45 the values of theprobability shown in Expression (2).

It should be clear that the probability generator 34 can easily accountfor the scaling factor described above with respect to Expression (4) bysuitably normalizing the probability values that it generates, althoughsuch normalizing is not explicitly shown in the drawings.

FIG. 5 illustrates exemplary operations which can be performed by thereceiver embodiments of FIGS. 3 and 4. At 51, initial a priori outputprobabilities are produced for the SISO decoders. This can be done, forexample, by the probability generator 34 calculating the values of theleftmost probabilities of Expressions (8) and (9) and summing thesevalues without multiplying by the rightmost probabilities of Expressions(8) and (9) (which rightmost probabilities are not yet available asfeedback from the SISOs). FIG. 5 assumes that the SISO decoder 35 isselected to operate first and begin the iterative process. However, theSISO 36 could also be selected to operate first and begin the iterativeprocess, and this possibility is therefore indicated by theparenthetical expressions in FIG. 5. The following textual descriptionof FIG. 5 assumes the aforementioned example of beginning with SISO 35.

At 52, SISO 35 uses the initial a priori output probabilities to producea posteriori input probabilities. At 53, interleaving is applied to thea posteriori input probabilities from SISO 35. At 54, SISO 36 uses theinitial (for the first iteration) a priori output probabilities and theinterleaved a posteriori input probabilities of SISO 35 to produce aposteriori input and output probabilities. At 55, de-interleaving isapplied to the a posteriori input probabilities from SISO 36. At 56, thea posteriori output probabilities from SISO 36 are used to produce apriori output probabilities for SISO 35. At 57, the SISO 35 uses its apriori output probabilities and the de-interleaved a posteriori inputprobabilities of SISO 36 to produce a posteriori input and outputprobabilities. At 58, the a posteriori output probabilities from SISO 35are used to produced a priori output probabilities for SISO 36. Theoperations at 53-58 are then repeated for any desired number ofiterations.

FIG. 6 diagrammatically illustrates further exemplary embodiments of awireless communication system according to the invention. In the systemof FIG. 6, the transmitter 61 is similar to the transmitter 11 of FIGS.1 and 3, but includes interleavers 63 and 64 at the outputs of theconvolutional coders. Thus, the receiver 62 includes a de-interleaver 65and an interleaver 66 to account for the operations of the interleaver63, and also includes a de-interleaver 67 and an interleaver 68 toaccount for the operation of the interleaver 64. Aside from theoperations of the interleavers and de-interleavers illustrated at 63-68,the wireless communication system of FIG. 6 can operate in generally thesame fashion as the wireless communication system of FIG. 3, that is,generally as described above with respect to FIG. 5.

FIG. 7 illustrates exemplary simulation results for the systems of FIG.1 (71), FIG. 3 (72), and FIG. 6 (73). As shown in FIG. 7, the FIG. 3system at 72 performs better (in terms of frame error rate FER) than theFIG. 1 system at 71, showing gains of about 2 dB at higher SNRs. TheFIG. 3 system also exhibits a noticeable increase in slope, so the gainscan be expected to be even larger at higher SNRs. The FIG. 6 system at73 provides an additional performance gain of about 1 dB at the higherSNRs, and also exhibits an increase in slope as compared to the systemof FIG. 1 at 71.

FIG. 9 diagrammatically illustrates pertinent portions of exemplaryembodiments of a wireless communication transmitter apparatus accordingto the invention. As shown in FIG. 9, the input bits received from acommunication application are encoded by a single convolutional coder91, and the encoded bits are interleaved by an interleaver 92. Thesymbols or bits X_(t) produced by the interleaver 92 and the symbols orbits Y_(t) produced by the encoder 91 are then modulated (for exampleusing QPSK) and transmitted by respective transmit antennas.

FIG. 10 diagrammatically illustrates pertinent portions of exemplaryembodiments of a wireless communication receiver apparatus that iscapable of receiving the wireless communication signals transmitted bythe wireless communication transmitter apparatus of FIG. 9. Theapparatus of FIG. 10 includes a probability generator 34 which can be,for example, identical to the probability generator 34 described abovewith respect to FIGS. 3-6. The a priori output probability valuesproduced at 45 by the probability generator 34 are applied to ade-interleaver 110 to account for the interleaver 92 in the transmitterapparatus of FIG. 9. The a priori output probability values produced at46 by the probability generator 34 are applied to a combiner 112 alongwith the output of the de-interleaver 110.

The combiner 112 is operable for combining the probability values at 46with the probability values output by the de-interleaver 110. In someexemplary embodiments, the combiner is simply a multiplier whichmultiplies the input probability values by one another. The combiner 112thus outputs combined a priori output probability values which representcombinations of the a priori output probability values input to thecombiner 112. The combined a priori output probability values at 114 areprovided to a SISO decoder 111. The SISO decoder 111 uses the combined apriori output probability values 114 to produce combined a posterioriinput and output probabilities. The combined a posteriori inputprobabilities are provided to a decision maker which decides the symbolvalues, and the combined a posteriori output probabilities are providedat 115 to a splitter 113.

The splitter 113 is operable for splitting each of the combined aposteriori output probability values at 115 into its constituentprobability values. The splitter output values 116, corresponding toprobability values 46, are provided to input 48 of the probabilitygenerator 34, and the splitter output values 117, corresponding to theprobability values at 45, are applied to an interleaver 92 (same as inFIG. 9) whose output is provided to the input 47 of the probabilitygenerator 34. In some exemplary embodiments, the splitter 113 is amarginal probability calculator which uses conventional techniques toextract, from the combined probability values at 115, constituentmarginal probability values corresponding to the probability values at45 and 46.

The decision maker can also utilize, for example, a splitter such asshown at 113 to split each of the combined a posteriori inputprobabilities into its constituent probability values. These constituentprobability values can then be used in conventional fashion to make thesymbol decisions.

FIG. 11 illustrates exemplary operations which can be performed by thewireless communication receiver apparatus of FIG. 10. At 120, theprobability generator 34 produces first and second sets of initial apriori output probabilities. At 121, de-interleaving is applied to thesecond set of a priori output probabilities. At 122, the first set of apriori output probabilities is combined with the de-interleaved secondset of a priori output probabilities to produce combined a priori outputprobabilities. At 123, the SISO decoder uses the combined a priorioutput probabilities to produce combined a posteriori input and outputprobabilities. At 124, the combined a posteriori output probabilitiesare split into first and second sets of a posteriori outputprobabilities. At 125, interleaving is applied to the second set of aposteriori output probabilities and, at 126, the first set and theinterleaved second set of a posteriori output probabilities are used bythe probability generator 34 to produce the next iteration of the secondand first sets of a priori output probabilities, respectively.Thereafter, the operations at 121-126 are repeated for any desirednumber of iterations.

FIG. 12 illustrates simulation results which compare the performance ofthe conventional system of FIG. 8 with the performance of the system ofFIGS. 9-11 according to the invention. In particular, the performance ofthe conventional system of FIG. 8 is illustrated at 130 and theperformance of the system of FIGS. 9-11 is illustrated at 131 (firstiteration), 132 (second iteration) and 133 (fifth iteration). Theperformance illustrated at 131, 132 and 133 was obtained using randominterleaving in the transmitter of FIG. 9 and the receiver of FIG. 10.

It will be apparent to workers in the art that any wirelesscommunication system that utilizes a space-time turbo code, or any kindof turbo code, can benefit from the present invention. Advantageously,the added complexity of the a posteriori output probability feedbackloops is relatively small compared to the complexity of a SISO block. Itwill also be apparent to workers in the art that the embodiments ofFIGS. 3-6 and 9-11 can be implemented, for example, by suitablemodifications in hardware, software, or a combination of hardware andsoftware, in conventional wireless communication transmitters andreceivers.

Although exemplary embodiments of the invention are described above indetail, this does not limit the scope of the invention, which can bepracticed in a variety of embodiments.

1. A wireless communication receiving apparatus, comprising: an antennafor receiving via first and second wireless communication channels acomposite communication symbol that represents first and secondcommunication symbols which each correspond to a result of a codingoperation performed by a transmitter apparatus on a bit stream; aprobability generator coupled to said antenna and responsive to saidcomposite communication symbol for generating, for said first and secondcommunication symbols, corresponding first and second pluralities ofprobabilities that the communication symbol has respective ones of aplurality of possible values of the communication symbol; a first SISOdecoder for receiving said first plurality of probabilities andproducing therefrom a further first plurality of probabilities, anoutput of said first decoder coupled to an input of said probabilitygenerator; a second SISO decoder for receiving said second plurality ofprobabilities and producing therefrom a further second plurality ofprobabilities, an output of said second decoder coupled to an input ofsaid probability generator; a de-interleaver coupling an output of saidfirst SISO decoder to an input of said second SISO decoder; and aninterleaver coupling an output of said second SISO decoder to an inputof said first SISO decoder.
 2. The apparatus of claim 1, wherein saidprobability generator further comprises an estimator coupled to receivesaid composite communication symbol.
 3. The apparatus of claim 2,wherein said estimator provides estimates of fading parameters fadingparameters in said composite communication symbol.
 4. The apparatus ofclaim 1, wherein said probability generator further comprises acalculation apparatus coupled to receive said composite communicationsymbol.
 5. The apparatus of claim 4, wherein said calculation apparatuscalculates probability values using the estimated fading parameters. 6.The apparatus of claim 2, wherein said probability generator furthercomprises a calculation apparatus coupled to receive said compositecommunication symbol.
 7. The apparatus of claim 6, further including atleast one input of said calculation apparatus being coupled to receiveestimated fading parameters from said estimator.
 8. The apparatus ofclaim 6, wherein said calculation apparatus calculates probabilityvalues using the estimated fading parameters.
 9. The apparatus of claim6, further including first and second combiners coupled to saidcalculation apparatus.
 10. The apparatus of claim 9, further includingan output of said first combiner coupled to an input of said first SISOdecoder and an output of said second combiner coupled to an input ofsaid second SISO decoder.
 11. The apparatus of claim 9, furtherincluding an input of said first combiner coupled to an output of saidsecond SISO decoder and an input of said second combiner coupled to anoutput of said first SISO decoder.
 12. The apparatus of claim 1, furtherincluding: a second de-interleaver coupling an output of saidprobability generator to an input of said second SISO decoder; a secondinterleaver coupling said output of said second decoder coupled to saidinput of said probability generator; a third de-interleaver coupling anoutput of said probability generator to an input of said first SISOdecoder; a third interleaver coupling said output of said first decoderto said input of said probability generator.
 13. The apparatus of claim1, wherein said first plurality of combined probabilities is received atan a priori output probability terminal of said first SISO decoder. 14.The apparatus of claim 13, wherein said further plurality of combinedprobabilities is a plurality of combined a posteriori outputprobabilities produced by said first SISO decoder.
 15. The apparatus ofclaim 1, wherein said second plurality of combined probabilities isreceived at an a priori output probability terminal of said second SISOdecoder.
 16. The apparatus of claim 15, wherein said further pluralityof combined probabilities is a plurality of combined a posteriori outputprobabilities produced by said second SISO decoder.
 17. A wirelesscommunication transmitter apparatus, comprising: an input for receivinga bit stream; a first coder coupled to said input for performing acoding operation on said bit stream, said coder having an output forproviding a result of said coding operation; a first interleaver coupledto said input, for interleaving said bit stream; a second coder, coupledto an output of said first interleaver, for performing a codingoperation on said interleaved bit stream, said coder having an outputfor providing a result of said coding operation; a second interleavercoupled to said first coder; a third interleaver coupled to said secondcoder; a first modulator coupled to an output of said second interleaverfor modulating said result, and a first antenna coupled to said firstmodulator for transmitting said modulated result of said first coderoperation on a wireless communication channel; and a second modulatorcoupled to an output of said third interleaver for modulating saidresult, and a second antenna coupled to said second modulator fortransmitting said modulated result of said second coder operation on awireless communication channel.
 18. The apparatus of claim 17, whereinat least one of said first and second coders is a convolutional coder.19. The apparatus of claim 17, wherein one of said first and secondmodulators is a QPSK modulator.
 20. A method of wireless communication,comprising: receiving a bit stream; performing a coding operation onsaid bit stream and outputting a result of said coding operation;interleaving said result of said coding operation; modulating saidinterleaved result with a first modulator and transmitting saidmodulated result on a first antenna; interleaving said bit stream;performing a coding operation on said interleaved bit stream andoutputting a result of said coding operation on said interleaved bitstream; interleaving said result of said coding operation on saidinterleaved bit stream; and modulating said interleaved result of saidcoding operation on said interleaved bit stream with a second modulatorand transmitting said modulated result on a second antenna.
 21. A methodof wireless communication, comprising: receiving via first and secondwireless communication channels a composite communication symbol thatrepresents first and second communication symbols which each correspondto a result of a coding operation performed by a transmitter apparatuson a bit stream; generating, for said first and second communicationsymbols, corresponding first and second pluralities of probabilitiesthat the communication symbol has respective ones of a plurality ofpossible values of the communication symbol; producing, from said firstplurality of probabilities, a further first plurality of probabilities,an output of said first decoder coupled to an input of said probabilitygenerator; and producing, from said second plurality of probabilities, afurther second plurality of probabilities, an output of said seconddecoder coupled to an input of said probability generator.
 22. Themethod of claim 21, wherein at least a portion of the results of saidstep of producing, from said first plurality of probabilities, a furtherfirst plurality of probabilities, are output to be used in saidgenerating step.
 23. The method of claim 21, wherein at least a portionof the results of said step of producing, from said second plurality ofprobabilities, a further second plurality of probabilities, are outputto be used in said generating step.